The present invention relates to a switchgear for opening/closing an electrical circuit and its operating mechanism and, more particularly, to a switchgear and its operating mechanism suitably configured for cutting off high-voltage current in short time periods.
In general, there are available, as an operating mechanism of a switchgear, one using a hydraulic operating force for large power and one using a spring operating force for middle/small output power. The former is referred to as “hydraulic operating mechanism” and the latter as “spring operating mechanism”. In recent years, the advancement of size reduction of an arc-extinguishing chamber of a gas-insulated circuit breaker which is a type of a switchgear allows fault current to be cut off with a smaller operating force, so that application of the spring operating mechanism becomes popular. However, a gas-insulated circuit breaker of extra high-voltage class requires high-speed operating capability called “2-cycle operation” that is capability of achieving cutoff within a time length corresponding to two-cycle time periods of alternating current. A conventional spring operating mechanism typically has operating capability equivalent to about 3-cycle operation, and it is not easy to realize the two-cycle cutoff capability due to poor responsiveness of a retention mechanism or retention control mechanism of a spring force.
A first type of conventional example of an operating mechanism of such a switchgear is disclosed in Japanese Patent Application Laid-Open Publications No. 11-213824 (FIGS. 1 and 7) and No. 2000-40445 (FIGS. 1 and 3), the entire contents of which are incorporated herein by reference. In operation mechanisms disclosed in these documents, a force of a cutoff spring is retained by a retention mechanism constituted by a latch, O-prop (opening-hook lever), and a catch through an output lever. In this configuration, when a trip current is applied to a solenoid serving as a retention control mechanism, a plunger of the solenoid activates the catch to allow the engagement between the catch and prop to be released, which releases the engagement between the output lever and the latch to rotate the output lever to release the cutoff spring force, thereby achieving cutoff operation.
A second type of conventional example of the switchgear operating mechanism is disclosed in Japanese Patent No. 3497866 (FIGS. 1 to 4), the entire content of which is incorporated herein by reference. In a spring operating mechanism disclosed in this document, a pull-out lever and a retention lever are provided for retaining a cutoff spring force. In this configuration, the retention lever is activated not by the cutoff spring force but by a force of an acceleration spring at the cutoff operation time so as to release the cutoff spring force.
In the first type of conventional example of the switchgear operating mechanism, operation for releasing the cutoff spring force (cutoff operation) is constituted by the following three steps: operation of the catch driven by excitation of the solenoid, operation of the O-prop, and operation of electrical contacts including the cutoff spring. The operational relationship between the above components is illustrated in FIG. 16. The horizontal axis denotes time, and vertical axis denotes a stroke of each components. In FIG. 16, the lowermost curve represents the waveform of a trip current and, above this, the stroke of the catch is depicted. Above this, the strokes of the O-prop and the cutoff spring are depicted. The uppermost curve represents an energizing signal of the contact in an arc-extinguishing chamber of a gas-insulated circuit breaker.
Time length from the start of application of the trip current until the operation of the O-prop is started along with the operation of the catch is assumed to be T1. Time length from the start of operation of the O-prop to the start of operation of the cutoff spring is assumed to be T2. Time length from the start of operation of the cutoff spring until the cutoff spring reaches its contact opening point is assumed to be T3. Assuming that contact opening time is T0,T0=T1+T2+T3  (1)is satisfied.
In order to realize 2-cycle operation, it is necessary to reduce contact opening time T0 to a given value. Thus, in a typical spring operating mechanism, operations of the components from the catch to the cutoff spring, which occur after the trip current application, are not started simultaneously. That is, the catch operates to some degree to release the engagement between itself and the O-prop to thereby allow operation of the O-prop to be started, and the cutoff spring starts operating after the O-prop operates to some degree. Thus, a mechanism that-retains a cutoff spring force operates in a stepwise manner, so that it is necessary to reduce respective time lengths T1, T2, and T3 in order to reduce T0.
However, since the cutoff spring force is determined by the weight of a movable portion of the arc-extinguishing chamber, opening speed, and drive energy, there is a limit to a reduction of T3. With regard to T2, weight reduction of the O-prop and increase in a force (retention force) of retaining the cutoff spring force allow high-speed operation of the O-prop. However, when the retention force is increased, the size of the O-prop needs to be increased for strength, which limits the weight reduction of the O-prop. It follows that there occurs a limit in the improvement in operation speed relying on the increase in the retention force. Further, when the retention force is increased, a large force is applied to the engagement portion between the O-prop and the catch, so that there occurs a need to increase the size of the catch for strength and to provide a solenoid having a large electromagnetic power for activating the catch.
At present, an excitation method using a large-sized condenser is adopted for obtaining a large power of the solenoid. However, the upper limit value for a current value flowing to the solenoid is specified in the standard, so that there is a limit in the improvement in the output power of the solenoid. As described above, it is difficult to reduce the contact opening time in the conventional spring operating mechanism.
Also in the second type of conventional example, operation for releasing the cutoff spring force is constituted by the following three steps: operation of a pull-off hook driven by an electromagnet; simultaneous operation of a reset lever, acceleration spring, and a retention lever; and simultaneous operation of a pull-off lever and a cutoff spring. In this example, the direction of a retention force (pressuring force) of the cutoff spring is made substantially coincident with the rotation center of the retention lever, thereby reducing a force required for the operation of the retention lever.
Further, the speed of movement of the retention lever, which is included in the above second step, is made higher by the accelerating spring to thereby reduce the operation time. However, it is physically difficult to reduce the operation time of the second step to zero and, therefore, it is difficult to significantly reduce the entire contact opening time, also in terms of the problems described in the first example.
Further, the direction of a pressuring force to a portion at which the pull-off lever and the retention lever are engaged with each other is made substantially coincident with the rotation center of the retention lever, so that when an external vibration is applied to the retention lever to force the same to vibrate, the pull-off lever is rotated in the cutoff operation direction, and the cutoff operating mechanism may start operating without a cutoff command.
Further, the direction of the pressuring force may fluctuate with respect to the rotation center of the retention lever due to deformation of the engagement surface between a roller provided on the pull-off lever and the retention lever, so that when the pressuring force acts in the cutoff operation direction of the retention lever, the pull-off lever may be released without a cutoff command.
Further, although not described in Japanese Patent No. 3497866, it is just conceivable that the retention lever operates in the cutoff direction due to an impact force applied when the roller pushes aside the retention lever for reengagement in the closing operation to allow the cutoff operation to be started without a cutoff command. As described above, in the second example, it is difficult to significantly reduce the contact opening time and it is likely that a retention state of the cutoff spring becomes unstable.
The present invention has been made to solve the above problems, and an object thereof is to provide a switchgear for opening/closing an electrical circuit and its operating mechanism in which retention/release of the cutoff spring force is performed by a combination of a latch and its lock mechanism to reduce a time period for the cutoff spring force to be released so as to significantly reduce the entire contact opening time and, at the same time, stability and reliability of a retention state of the cutoff spring force are improved.